Synonyms in many situations with nuanced differences. :

prédire implies stating/announcing that something is expected to occur; this may be based just on supposition but could also be after deliberation

prévoir implies a more structured, rational approach to determining a likely event/outcome which may or may not be broadcast prior to the event but often is eg the weather, business outcomes etc 

Not an exact match by any means, but in English it might help to think of the overlap and differences between ‘predict’ and ‘preview’.

https://vitrinelinguistique.oqlf.gouv.qc.ca/23855/le-vocabulaire/nuances-semantiques/difference-entre-predire-et-prevoir